Osami Yukawa

Induction of radioresistance to accelerated carbon-ion beams in recipient cells by nitric oxide excreted from irradiated donor cells of human glioblastoma.

Purpose : To investigate whether nitric oxide excreted from cells irradiated with accelerated carbon-ion beams modulates cellular radiosensitivity against irradiation in human glioblastoma A-172 and T98G cells. Materials and methods : Western-blot analysis of inducible nitric oxide synthase, hsp72 and p53, the concentration assay of nitrite in medium and cell survival assay after irradiation with accelerated carbon-ion beams were performed. Results : The accumulation of inducible nitric oxide synthase was caused by accelerated carbon-ion beam irradiation of T98G cells but not of A-172 cells. The accumulation of hsp72 and p53 was observed in A-172 cells after exposure to the conditioned medium of the T98G cells irradiated with accelerated carbon-ion beams, and the accumulation was abolished by the addition of an inhibitor for inducible nitric oxide synthase to the medium. The radiosensitivity of A-172 cells was reduced in the conditioned medium of the T98G cells irradiated with accelerated carbonion beams compared with conventional fresh growth medium, and the reduction of radiosensitivity was abolished by the addition of an inducible nitric oxide synthase inhibitor to the conditioned medium. Conclusions : Nitric oxide excreted from the irradiated donor cells with accelerated carbon-ion beams could modulate the radiosensitivity of recipient cells. These findings indicate the importance of an intercellular signal transduction pathway initiated by nitric oxide in the cellular response to accelerated heavy ions.PURPOSE To investigate whether nitric oxide excreted from cells irradiated with accelerated carbon-ion beams modulates cellular radiosensitivity against irradiation in human glioblastoma A-172 and T98G cells. MATERIALS AND METHODS Western-blot analysis of inducible nitric oxide synthase, hsp72 and p53, the concentration assay of nitrite in medium and cell survival assay after irradiation with accelerated carbon-ion beams were performed. RESULTS The accumulation of inducible nitric oxide synthase was caused by accelerated carbon-ion beam irradiation of T98G cells but not of A-172 cells. The accumulation of hsp72 and p53 was observed in A-172 cells after exposure to the conditioned medium of the T98G cells irradiated with accelerated carbon-ion beams, and the accumulation was abolished by the addition of an inhibitor for inducible nitric oxide synthase to the medium. The radiosensitivity of A-172 cells was reduced in the conditioned medium of the T98G cells irradiated with accelerated carbon-ion beams compared with conventional fresh growth medium, and the reduction of radiosensitivity was abolished by the addition of an inducible nitric oxide synthase inhibitor to the conditioned medium. CONCLUSIONS Nitric oxide excreted from the irradiated donor cells with accelerated carbon-ion beams could modulate the radiosensitivity of recipient cells. These findings indicate the importance of an intercellular signal transduction pathway initiated by nitric oxide in the cellular response to accelerated heavy ions.

Radiation-induced Lipid Peroxidation and Membrane-bound Enzymes in Liver Microsomes

Changes in lipid peroxidation and enzymes in liver microsomes were examined after alpha-irradiation. The radiation-induced lipid peroxidation was increased with increasing radiation dose, with decreasing dose-rate and also with decreasing concentration of microsomes. The content of P-450 was decreased with decreasing dose-rate and inversely with radiation dose, while NADPH-cytochrome c reductase and cytochrome b5 were less affected by alpha-irradiation. Both the lipid peroxidation and the inactivation of microsomal enzymes induced by alpha-irradiation were mardedly reduced by radical scavengers. Hexobarbital hydroxylating activity and binding capacity of P-450 for hexobarbital, which were strikingly decreased after alpha-irradiation were less protected by radical scavengers, in contrast to the case of the lipid peroxidation and of the enzymes. These results suggest that intrinsic enzymes are more damaged through radiation-induced peroxidation of membrane lipids as compared with extrinsic enzymes.

Adaptive response in embryogenesis : I. Dose and timing of radiation for reduction of prenatal death and congenital malformation during the late period of organogenesis

An adaptive response was demonstrated during embryogenesis in mice. Whole-body irradiation at a dose of 0-50 cGy was given to condition pregnant ICR mice on day 9 to day 11 of gestation. Then their whole bodies were exposed to a challenging dose of 5 Gy on the next day. The numbers of living fetuses, prenatal deaths and living fetuses with external gross malformations were determined on day 19. A conditioning dose of 30 cGy on day 11 significantly increased the rate of living fetuses and reduced the incidence of congenital malformations induced by a 5-Gy dose on day 12. This indicates the existence of a critical dose and timing for administering a conditioning dose for radioadaptation during the late period of organogenesis in mice. The possible mechanisms involved are discussed.

Reconstitution Studies on the Involvement of Radiation-induced Lipid Peroxidation in Damage to Membrane Enzymes

The effect of radiation on the drug-metabolizing enzyme system of microsomes, reconstituted with liposomes of microsomal phospholipids, NADPH-cytochrome P-450 reductase and cytochrome P-450, was examined to elucidate the role of lipid peroxidation of membranes in radiation-induced damage to membrane-bound enzymes. The reconstituted system of non-irradiated enzymes with irradiated liposomes showed a low activity of hexobarbital hydroxylation, whereas irradiated enzymes combined with non-irradiated liposomes exhibited an activity equal to that of unirradiated controls. Irradiation of liposomes caused a decrease in cytochrome P-450 content by destruction of the haem of cytochrome P-450 and also inhibited the binding capacity of cytochrome P-450 for hexobarbital. The relationship between radiation-induced lipid peroxidation and membrane-bound enzymes is discussed.

Adaptive Response in Embryogenesis. III. Relationship to Radiation-Induced Apoptosis and Trp53 Gene Status

Abstract Wang, B., Ohyama, H., Haginoya, K., Odaka, T., Itsukaichi, H., Yukawa, O., Yamada, T. and Hayata, I. Adaptive Response in Embryogenesis. III. Relationship to Radiation-Induced Apoptosis and Trp53 Gene Status. We reported previously that a radiation-induced adaptive response existed in the late period of embryogenesis, and that radiation-induced apoptosis in the predigital regions was responsible for digital defects in embryonic ICR mice. To investigate the possible involvement of the Trp53 gene and radiation-induced apoptosis in radiation-induced adaptive responses in embryogenesis, the present study was conducted using Trp53 wild-type (Trp53+/+) and Trp53 heterozygous (Trp53+/–) embryonic mice of the C57BL/6 strain. The existence of a radioadaptive response in the Trp53+/+ embryonic mice was demonstrated by irradiating the embryos with 5 or 30 cGy on embryonic day 11 prior to a challenging irradiation at 3 Gy on embryonic day 12. The two conditioning doses at 5 and 30 cGy significantly suppressed the induction of apoptosis by the challenging dose in the predigital regions of limb buds in the Trp53+/+ embryonic mice, while no such effect was found in the Trp53+/– embryonic mice. These findings indicate that induction of a radioadaptive response in embryogenesis is related to Trp53 gene status and the occurrence of radiation-induced apoptosis.

Adaptive Response in Embryogenesis: V. Existence of Two Efficient Dose-Rate Ranges for 0.3 Gy of Priming Irradiation to Adapt Mouse Fetuses

Abstract Wang, B., Ohyama, H., Shang, Y., Tanaka, K., Aizawa, S., Yukawa, O. and Hayata, I. Adaptive Response in Embryogenesis: V. Existence of Two Efficient Dose-Rate Ranges for 0.3 Gy of Priming Irradiation to Adapt Mouse Fetuses. Radiat. Res. 161, 264–272 (2004). The adaptive response is an important phenomenon in radiobiology. A study of the conditions essential for the induction of an adaptive response is of critical importance to understanding the novel biological defense mechanisms against the hazardous effects of radiation. In our previous studies, the specific dose and timing of radiation for induction of an adaptive response were studied in ICR mouse fetuses. We found that exposure of the fetuses on embryonic day 11 to a priming dose of 0.3 Gy significantly suppressed prenatal death and malformation induced by a challenging dose of radiation on embryonic day 12. Since a significant dose-rate effect has been observed in a variety of radiobiological phenomena, the effect of dose rate on the effectiveness of induction of an adaptive response by a priming dose of 0.3 Gy administered to fetuses on embryonic day 11 was investigated over the range from 0.06 to 5.0 Gy/min. The occurrence of apoptosis in limb buds, incidences of prenatal death and digital defects, and postnatal mortality induced by a challenging dose of 3.5 Gy given at 1.8 Gy/min to the fetuses on embryonic day 12 were the biological end points examined. Unexpectedly, effective induction of an adaptive response was observed within two dose-rate ranges for the same dose of priming radiation, from 0.18 to 0.98 Gy/ min and from 3.5 to 4.6 Gy/min, for reduction of the detrimental effect induced by a challenging dose of 3.5 Gy. In contrast, when the priming irradiation was delivered at a dose rate outside these two ranges, no protective effect was observed, and at some dose rates elevation of detrimental effects was observed. In general, neither a normal nor a reverse dose- rate effect was found in the dose-rate range tested. These results clearly indicated that the dose rate at which the priming irradiation was delivered played a crucial role in the induction of an adaptive response. This paper provides the first evidence for the existence of two dose-rate ranges for the same dose of priming radiation to successfully induce an adaptive response in mouse fetuses.

Effect of chronic HTO. beta. or /sup 60/Co. gamma. radiation on preimplantation mouse development in vitro

Response of pronuclear, early 2-cell, and late 2-cell mouse embryos to chronic HTO β and60 Co γ irradiation was investigated. The pronuclear embryos fertilized in vitro and 2-cell stage embryos of ...

Adaptive response in embryogenesis: IV. Protective and detrimental bystander effects induced by X radiation in cultured limb bud cells of fetal mice.

Abstract Wang, B., Ohyama, H., Shang, Y., Fujita, K., Tanaka, K., Nakajima, T., Aizawa, S., Yukawa, O. and Hayata, I. Adaptive Response in Embryogenesis: IV. Protective and Detrimental Bystander Effects Induced by X Radiation in Cultured Limb Bud Cells of Fetal Mice. Radiat. Res. 161, 9–16 (2004). The radioadaptive response and the bystander effect represent important phenomena in radiobiology that have an impact on novel biological response mechanisms and risk estimates. Micromass cultures of limb bud cells provide an in vitro cellular maturation system in which the progression of cell proliferation and differentiation parallels that in vivo. This paper presents for the first time evidence for the correlation and interaction in a micromass culture system between the radioadaptive response and the bystander effect. A radioadaptive response was induced in limb bud cells of embryonic day 11 ICR mice. Conditioning irradiation of the embryonic day 11 cells with 0.3 Gy resulted in a significant protective effect against the occurrence of apoptosis, inhibition of cell proliferation, and differentiation induced by a challenging dose of 5 Gy given the next day. Both protective and detrimental bystander effects were observed; namely, irradiating 50% of the embryonic day 11 cells with 0.3 Gy led to a successful induction of the protective effect, and irradiating 70% of the embryonic day 12 cells with 5 Gy produced a detrimental effect comparable to that seen when all the cells were irradiated. Further, the bystander effect was markedly decreased by pretreatment of the cells with an inhibitor to block the gap junction-mediated intercellular communication. These results indicate that the bystander effect plays an important role in both the induction of a protective effect by the conditioning dose and the detrimental effect of the challenge irradiation. Gap junction-mediated intercellular communication was suggested to be involved in the induction of the bystander effect.

Rescue of Lethally Irradiated Mice from Hematopoietic Death by Pre-exposure to 0.5 Gy X Rays without Recovery from Peripheral Blood Cell Depletion and its Modification by OK432

Abstract Nose, M., Wang, B., Itsukaichi, H., Yukawa, O., Hayata, I., Yamada, T. and Ohyama, H. Rescue of Lethally Irradiated Mice from Hematopoietic Death by Pre-exposure to 0.5 Gy X Rays without Recovery from Peripheral Blood Cell Depletion and its Modification by OK432. Radiat. Res. 156, 195–204 (2001). Exposing mice to 0.5 Gy X rays 2 weeks before lethal irradiation has been reported to induce marked radioresistance and to rescue them from hematopoietic death. Here we examined effects of the 0.5-Gy pre-exposure on hematological changes in C57BL mice that were lethally irradiated with 6.5 Gy X rays. Approximately 77% of pre-exposed mice survived 30 days after this irradiation, whereas 80% of mice that did not receive this pre-exposure died by day 20. However, regardless of the pre-exposure, peripheral blood cell counts decreased markedly by day 3 and reached a nadir at day 20. CFU-S in femur and CFU-GM in spleen had started to recover at day 10 and 14, respectively, but recovery of functional peripheral blood cells occurred later. The effect of pre-exposure on survival was altered by OK432, a bioresponse modifier; the effect depended on the timing of its administration. OK432 given 2 days before 0.5 Gy enhanced the protective effect of pre-exposure, resulting in the survival of 97% of the mice. In contrast, injection of OK432 1 day before or 2 days after pre-exposure led to 100% mortality. Thus the survival-promoting effect of 0.5 Gy could be altered by OK432. The OK432-induced changes in the survival of mice could not be attributed solely to hematological changes, as shown by blood cell counts and progenitor cell contents. These results suggest that radioresistance induced by pre-exposure to 0.5 Gy X rays is not stable, but rather varies with the physiological conditions, and can be modulated by factors such as OK432.

The dependence of p53 on the radiation enhancement of thermosensitivity at different let

PURPOSE The aim of this study is to investigate the dependence of p53-gene status on the radiation enhancement of thermosensitivity at different levels of linear energy transfer (LET). METHODS AND MATERIALS We used two kinds of human glioblastoma transfectants of A-172 cells bearing the wild-type p53 gene, A-172/neo cells with control vector containing the neo gene and A-172/mp53 cells with both the dominant negative mutated p53 gene and neo gene. We exposed these cells to X-rays and accelerated carbon-ion (C-) beams (13-200 KeV/microm) followed by heating at 44 degrees C. Cellular sensitivities were determined using clonogenic assay. RESULTS The radiation enhancement of thermosensitivity was LET-dependent for the A-172/neo cells, but this was not clearly demonstrated in the A-172/mp53 cells. The supraadditive radiation enhancement of thermosensitivity was observed in A-172/neo cells at the LET range of 13 to 70 KeV/microm, though only an additive effect was observed at higher LET. In A-172/mp53 cells, only an additive effect was observed through all the LET examined. CONCLUSION These results indicate that the radiation enhancement of thermosensitivity is p53- and LET-dependent. Our results suggest that the combined use of high-LET radiation and hyperthermia brings useful application for cancer therapeutic purposes.